RGCMDS “Row Graphics compression Commands”.
SIZE: 207 bytes.

ID #92
  01 CPRSRG$($)
  02 EXPDRG$($)

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These functions are for compressing (packing)
and expanding (unpacking) graphic strings for
more efficient storage.

Originally used with the ThinkJet Space
Shuttle demo by HP.

CPRSRG$(A$), read "ComPReSs Row-Graphic
String" searches A$ for null bytes [CHR$(0)]
and replaces them all with a single null fol-
lowed by a count byte.  This usually gives
a shorter string than the original one, but
can result in a longer one if the original
contains many single nulls.  The greatest
efficiency is obtained with strings
containing many nulls in a row (graphic white
space).

EXPDRG$(A$), read "EXPanD Row-Graphic String"
expands a compressed string back to its
original contents by looking for any null
and replacing it with as many nulls as the
next byte indicates.

Non-graphic data seldom contains nulls, so
packing them with RGCMDS is inefficient.
A lexfile designed for packing ASCII text
is called SPACKLX (464 bytes) and uses an
algorithm optimized for strings composed of a
narrow range of byte values, which most non-
graphics data contain.